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ljk4-1
Any serious plans to send a probe into the Sun to explore its depths as far as possible?

What would help a probe last as long as it could and how deep could it get?

Could it even radio or laser out any data?

What about a Sun skimmer?
nprev
I don't know, but my best guess would be <poof!!!> before any such probe even got close to the photosphere, so I doubt that any useful data could be gathered even if it could somehow be transmitted through all that RF noise... cool.gif (need shades just to think about it!!!)
JRehling
Solar Probe was supposed to come within 3 solar radii.

I suppose an elaborately shaded craft could get pretty close. A "ball" with instruments could be surrounded with a hemispherical shade with near 100% reflectance held by struts rather far from the craft. Perhaps even a hierarchical tier of such shades could perform even better.

Entering the photosphere would instantly annihilate any craft. The velocity of the craft as it hit the outer layers of gas, which would increase rapidly in pressure with depth, would be colossal -- even aside from the radiative heat.
dvandorn
Well, there's always David Brin's solution. Use a laser to *refrigerate* the probe, and to provide braking thrust against the Sun's gravity.

The idea is to drain the thermal energy into a system that powers a very powerful, very HOT laser. This would be the *only* way to use a "radiator" to shed heat into the photosphere.

A side benefit would be that such a laser would exert *significant* thrust, and it would be aimed at a target that it couldn't much hurt -- the Sun's surface.

The catch, of course, is that we really don't have the technology to build such a hot laser, or to convert the heat we can't reflect away into power for the laser. Once we develop those technologies (if we ever do), then a solar probe is more feasible...

-the other Doug
Richard Trigaux
QUOTE (JRehling @ Dec 25 2005, 06:15 AM)
Solar Probe was supposed to come within 3 solar radii.

I suppose an elaborately shaded craft could get pretty close. A "ball" with instruments could be surrounded with a hemispherical shade with near 100% reflectance held by struts rather far from the craft. Perhaps even a hierarchical tier of such shades could perform even better.

Entering the photosphere would instantly annihilate any craft. The velocity of the craft as it hit the outer layers of gas, which would increase rapidly in pressure with depth, would be colossal -- even aside from the radiative heat.
*


Yes, if we imagine a shield, the shape of a ... shield, which shadow comes up on the probe itself, in such a way that it just eclips the Sun and, seen from the probe, appears like a disk just a bit larger than the Sun (like the Moon just eclips the Sun seen from Earth) then this shield gets very hot, indeed, but, seen from the probe, it appears as a circle just a bit larger than the Sun but not so hot. The reason is that it absorbs Sun heat from one side, but it radiates its own heat on both sides. So it can provide an efficient shadowing. And a tiered structure of such shields can really efficiently cut down the heat received by the probe itself in one or two orders of magnitude.
So we can get much closer from the Sun than with any other design. The limitation is the first shield (the shield size quickly increases with the number of tiers) which must be made of very high fusion point material and be polished so what it reflects as much heat as possible without aborbing it. The only solution I see would be a very thin veil of tungsteen, polished in front and blackened with graphite at the rear. The second, third etc. tiers would be conical in shape, to increase side radiation.

Such a design would allow to get very close from the Sun, much closer than Mercury, and, if we give the shield a slightly parabolic shape, it can also be used as a high gain antenna, and contribute to overcome the very poor signal/noise ratio.

Getting closer? The capture speed near the Sun is more than 600km/s, and this figure alone is detering: even if a probe manages to cope with the radiated heat, as soon as it will enter the corona it will drag and burn. Remember: the coldest place on the Sun is 4000°C (in spots) where tungsteen and graphite cannot bear much more than 3000°C. So, unless there is some very new and unexpected discovery in physics, we are bound to contemplate the Sun from afar.

The laser to cool the probe? Whatever its technology, a laser produces waste heat. And, unless we find a way to get around the second principe of thermodynamics, we cannot use it to cool anything. The only way to cool a probe would be to bring a lot of water, and make it boil to regrigerate the probe for a short time, before it gets too hot. Even one hour gained at 600km/s would allow to gain two Sun radii. But, very close from the Sun, the heat is enough to boil a full swimming pool of water in some seconds...
Richard Trigaux
Other ways to probe the Sun would be sending a laser ray or radio beam. Unfortunately, the Sun is opaque to both. At best we can imagine passing very close to the surface (from a probe to the Earth). We can imagine to send very low radio frequencies, but I am afraid that the time constants involved would be thousands of years. (Already on Earth probing the core with radio waves would require frequencies too low to be actualy useable).


Impossible, impossible, impossible...

So why not the most impossible of all: SUN SAMPLE RETURN MISSION!!!!

Ouah nutter and nutter!!

But paradoxically it is the simplest to do, and it was even already done, with this probe, I did not remember the name, perhaps Stardust, which went in space to capture solar wind dust, and then crashed at time of return on Earth, but all the same produed useable samples of Sun composition.

But they took no measure against contamination of Earth by Sun life form... wink.gif
nprev
The only "practical" solution I can see would be to embed a probe and several layers of redundant sensors at the dead center of a rather large comet nucleus or maybe one of Saturn's smaller icy moons and deorbit the whole thing right into the Sun using a lot of ion thrusters or perhaps mass drivers, if there was enough metallic material available to use as reaction mass...

I doubt that the value of data retrieved would ever equal the investment, though, even if all the assumed supporting technologies were ever available. Remote sensing is far better in all respects!
Jyril
QUOTE (Richard Trigaux @ Dec 25 2005, 11:36 AM)
But paradoxically it is the simplest to do, and it was even already done, with this probe, I did not remember the name, perhaps Stardust, which went in space to capture solar wind dust, and then crashed at time of return on Earth, but all the same produed useable samples of Sun composition.


The Genesis mission... It was to be captured from mid-air, because a parachute landing would have been too hard. wink.gif
Richard Trigaux
QUOTE (Jyril @ Dec 25 2005, 12:22 PM)
The Genesis mission... It was to be captured from mid-air, because a parachute landing would have been too hard. wink.gif
*


Yes it was that. Pity the chute did not open. So the landing WAS hard. But the scientists managed to recollect most of the science data.
tty
A lot of neutrinos from the interior of the Sun is passing through Earth all the time, so all we need to see into the Sun is a good neutrino telescope. smile.gif

tty
Richard Trigaux
QUOTE (tty @ Dec 25 2005, 04:37 PM)
A lot of neutrinos from the interior of the Sun is passing through Earth all the time, so all we need to see into the Sun is a good neutrino telescope.  smile.gif

tty
*


We don't have a "good neutrino telescope". But what we have already learned much about the inner Sun. And about the neutrinos...


I am sorry, I usually have plenty of ideas to do things most people think impossible, but about plunging INTO the Sun, I don't have!
BruceMoomaw
Richard Trigaux, alas, is too optimistic about the Genesis scientists being able to retrieve "most" of their planned data. The latest news is that they will indeed be able to properly measure the amount of noble gases in the Sun, since those (except for argon-40, which is irrelevant) exist only in microscopic amounts in Earth's atmosphere and water, and so weren't affected by the crash's contamination. But that was only their third scientific priority -- the top ones were to measure the isotopic ratios of the Sun's oxygen and nitrogen (especially the former), and unfortunately those have been very badly contaminated indeed. It's questionable whether they'll be able to retrieve any meaningful results on those.

As for Solar Probe -- whose design has been modestly changed lately, without harming its total science output -- see the very informative official Web page at http://solarprobe.gsfc.nasa.gov/ . Solar scientists would absolutely love to fly this mission, but it will cost as much as a New Frontiers mission and so NASA has yet even to officially propose it. (It's even been suggested that it should be included in the New Frontiers program. But that, in turn raises the question of whether ALL competitive-proposal programs for space science -- Solar System, Mars, astronomy, magnetospheric science or what have you -- that are in the same cost range should be folded up together into a single competitive space-science proposal program, which might well make sense.)

There is no doubt at all, however, that we can make Solar Probe work -- amazingly, we already have almost all the technology we need for it. Extensive ground tests of that dunce-cap shaped carbon heat shield show that not only does it provide full protection against the heat, but it vaporizes considerably less than expected and so won't contaminate the probe's plasma measurements. The only thing that requires any additional work at this point is the design for the "plasma periscope" that would peep around the edge of the heat shield and divert a small amount of the outflowing solar plasma to the analyzers behind the shield.
Richard Trigaux
QUOTE (BruceMoomaw @ Dec 25 2005, 11:23 PM)
Richard Trigaux, alas, is too optimistic about the Genesis scientists being able to retrieve "most" of their planned data.  The latest news is that they will indeed be able to properly measure the amount of noble gases in the Sun, since those (except for argon-40, which is irrelevant) exist only in microscopic amounts in Earth's atmosphere and water, and so weren't affected by the crash's contamination.  But that was only their third scientific priority -- the top ones were to measure the isotopic ratios of the Sun's oxygen and nitrogen (especially the former), and unfortunately those have been very badly contaminated indeed.  It's questionable whether they'll be able to retrieve any meaningful results on those.
*


The team first came with an optimistic statement, pity of it did not worked. There was many expectations about this experiment.




QUOTE (BruceMoomaw @ Dec 25 2005, 11:23 PM)
As for Solar Probe -- whose design has been modestly changed lately, without harming its total science output -- see the very informative official Web page at  http://solarprobe.gsfc.nasa.gov/ .  Solar scientists would absolutely love to fly this mission, but it will cost as much as a New Frontiers mission and so NASA has yet even to officially propose it.  (It's even been suggested that it should be included in the New Frontiers program.  But that, in turn raises the question of whether ALL competitive-proposal programs for space science -- Solar System, Mars, astronomy, magnetospheric science or what have you -- that are in the same cost range should be folded up together into a single competitive space-science proposal program, which might well make sense.)

There is no doubt at all, however, that we can make Solar Probe work -- amazingly, we already have almost all the technology we need for it.  Extensive ground tests of that dunce-cap shaped carbon heat shield show that not only does it provide full protection against the heat, but it vaporizes considerably less than expected and so won't contaminate the probe's plasma measurements.  The only thing that requires any additional work at this point is the design for the "plasma periscope" that would peep around the edge of the heat shield and divert a small amount of the outflowing solar plasma to the analyzers behind the shield.
*


So there is REALLY such a project?

Woww.

Thank you for the link, Bruce, it is very interesting. I hope such a mission will fly one day.

Of course at only 4 sun radii of the surface of the sun, it will be unmanned. Not yet any Bush plan for Sun colonization?

And for the great dive INTO the Sun, we shall see a bit later.
edstrick
Unfortunately, the Solar Probe mission, or whatever it's name of the year is... has seemed to always be 10 years in the future. Rather like "Main Belt Multi Asteroid Rendezvous", which has been repeat-studied and repeat-proposed since the early 70's. If <whimper> Dawn flies, we'll finally get that one.
ljk4-1
QUOTE (Richard Trigaux @ Dec 26 2005, 04:27 AM)
The team first came with an optimistic statement, pity of it did not worked. There was many expectations about this experiment.
So there is REALLY such a project?

Woww.

Thank you for the link, Bruce, it is very interesting. I hope such a mission will fly one day.

Of course at only 4 sun radii of the surface of the sun, it will be unmanned. Not yet any Bush plan for Sun colonization?

And for the great dive INTO the Sun, we shall see a bit later.
*


Maybe if we tell Bush there's a lot of oil on the Sun....
Richard Trigaux
QUOTE (ljk4-1 @ Dec 26 2005, 06:03 PM)
Maybe if we tell Bush there's a lot of oil on the Sun....
*


Yes, there is plenty, it is called solar energy.
antoniseb
It would be possible to create a probe that could reach the photosphere, and continue into the body of the Sun a short way. There is a lot of question as to how it might communicate out of the Sun. Communication might be possible with x-ray lasers. Anything with a lower photon energy might get absorbed pretty quickly by the plasma.

This is not a realistic plan for the short term future, but you can imagine a craft that has a mass of billions of tons, and has a mechanism for spraying an opaque cloud out in front of it to shield the vessel with disposable shielding. Alternatively, or in addition, you might have a conveyer belt of rigid shielding that only exposes the individual tiles to the Sun for a small fraction of the time. Excess heat is blown off in the opaque jets previously described, or used to heat gases to thrust out the back.

The Photosphere's density is very low. It would take quite a while for a billion ton object to be vaporized if it was well designed. Just as a wild guess, such a craft could potentially descend a thousand miles.
dvandorn
QUOTE (Richard Trigaux @ Dec 26 2005, 02:52 PM)
Yes, there is plenty (of oil on the sun - Ed.), it is called solar energy.
*

Absolutely. After all, fossil fuels are nothing more than storage units for solar energy.

-the other Doug
BruceMoomaw
The trouble is that we haven't as yet come up with a way to collect and store it that's even remotely as efficient as utilizing -- at breakneck pace -- the fossil fuels that Mother Nature thoughtfully spent hundreds of millions of years accumulating for us. Talk about spendthrift heirs!

As for solar astronomy missions -- including Solar Probe -- they may have genuine practical importance. We need to know more about the Sun's longer-term activity cycles, in order to judge what effects those will have on Earth's climate that will be overlaid on top of the effects from the buildup of man-made greenhouse gases.

And, yep, the idea of Solar Probe has been around for a long, long time. Back in the early 1980s it was a big hulking thing called Starprobe that weighed thousands of kg and would have had to be launched by a Titan. Then, in the early 1990s, someone developed a way of greatly shrinking it by shaping the heat shield in such a way that it doubled as the probe's high-gain antenna. Still later, however, it became clear that electronic miniaturization has advanced to the point that we don't need that peculiar idea to build a lightweight version of Solar Probe. As with ion drives, We Have The Technology, and the only thing stopping us from doing it is the cost.

And Congress itself has repeatedly expressed some interest in this mission, and at least twice has inserted an additional $10 million into NASA's budget -- which NASA hadn't asked for -- for design studies. At some point, it WILL fly. (The analogy that comes to mind is SIRTF, which got delayed repeatedly, but in the process underwent technological evolution that both drastically reduced its cost AND increased its science output. And finally, it did fly, as the extremely successful Spitzer Space Telescope.)

One of the more mind-boggling things about this mission, by the way, is that one of its goals is to take images of the solar corona -- from inside the corona, looking out.
BlackMage
Well, if one gets to think into the really long-range future (think decades), then a Solar Sample Return mission from the corona (or even the photosphere, if you want to get REALLY fanciful) might finally find a use for Bussard's beautiful yet cosmically inefficient ramjet.

Use electromagnetic fields to collect hydrogen from the corona to fuel a fusion rocket, in order to collect samples and fly back to Earth. It'd be a project of stunning magnitude-thousands of tonnes, probably-but what's a few billion to a thought experiment?
tty
QUOTE (dvandorn @ Dec 27 2005, 08:25 AM)
Absolutely.  After all, fossil fuels are nothing more than storage units for solar energy.

-the other Doug
*


So is uranium, though from an earlier stellar generation.

tty
Bob Shaw
(Sigh)

You're all missing the obvious way to design a Solar Probe, although ISA already described a most persuasive mission scenario.

Just build one and launch it at night!

(Ducks and runs!)

Bob Shaw
Bob Shaw
QUOTE (Bob Shaw @ Dec 28 2005, 01:05 PM)
(Sigh)

You're all missing the obvious way to design a Solar Probe, although ISA already described a most persuasive mission scenario.

Just build one and launch it at night!

(Ducks and runs!)

Bob Shaw
*


Sorry, I forgot - ISA is the Irish Space Agency. Actually, they were going to send three spacecraft originally, with two levels of redundancy. To be sure, to be sure!

(Ducks, runs, and hides up a tree)

Bob Shaw
edstrick
A limitless, though relatively small, source of energy is the mouth-flapping of "zero-point energy" and the like folks. Considerably more abundant is the hot-air from politicians and we-know-what's-best-for-you advocates.
kwan3217
I recall a sci fi story from long ago about a manned station and manned boats on the surface of the sun. The three main obstacles to operating on the surface of the sun are:

1) intense heat
2) no solid surface
3) 32G surface gravity

The solutions are as follows

1) Carry a large supply of carbon, and pump it out of the surface of your platform. The carbon vaporizes and carries off the heat. Use carbon since it has the highest known melting and vaporization temperature of any substance. It acts like an ablative heat shield, or as the story described it, the bottom layer of a water drop in a hot pan.
2) Carry a big particle accelerator torus, and put a bunch of plasma in it and run it around the right direction such that it generates a magnetic field counter to the sun's magnetic field. If it is strong enough and controlled well enough, it will support the platform
3) Put this torus on the roof of the platform. Run the torus fast enough that through special relativity it gains enough mass to generate a 31G field in the up direction.

In the story, the mission of the platform and boats was to induce precisely controlled solar flares which would impact the atmosphere of the Earth, and in this manner they could control the weather. There was a vast representative democracy back on Earth, the Weather Congress, to decide what weather to have. There was a vast scientific institue, the Weather Advisors, to figure out how to implement the decisions of the Weather Congress. And there was the Weather Service, manning the base and boats on the sun, to carry out the plans of the Weather Advisors.

Now I know that there are dozens of reasons why the solutions proposed could not work (Where does all the carbon come from? What is the power source? What about tides from the gravity generator? Can you really use a plasma torus like that? The photosphere is hundreds of miles thick. Solar flares can't really influence Earth's weather that much. Even an enormous nuke is a mere sparkler on the sun, flares can't be induced.) but it is still interesting that someone actually considered a solution for landing on the sun which doesn't involve landing at night.
Richard Trigaux
QUOTE (edstrick @ Dec 28 2005, 12:30 PM)
Considerably more abundant is the hot-air from politicians and we-know-what's-best-for-you advocates.
*


perhaps it is this which creates climate change. We could eventually find a linear relationship between the temperature increase and the number of forgotten promises by politicians.
BruceMoomaw
That story was Theodore Taylor's "The Weather Man". Interesting idea, but even at age 12 it struck me as being a wee bit implausible. (He later wrote a sequel involving a suicidal trip to the CENTER of the Sun to stop an instability therein.)
Richard Trigaux
PINK FLOYD


SET THE CONTROL FOR THE HEART OF THE SUN
BruceMoomaw
So THAT'S how they got so pink.

By the way, Solar Probe originally started out as one of that very unlikely trinity of missions that were set up under Goldin's tenure to supposedly develop the new technologies necessary to go to "the most difficult destinations in the Solar System" -- along with Europa Orbiter and the Pluto flyby. This program was commonly called "Fire & Ice", but had the awkward official name of "Outer Planets/Solar Probe". (Back in 1999 I wrote to Chris Chyba suggesting that it needed a better name, and proposing -- roll of drums -- "New Frontier". He was noncommittal. Alan Stern later told me that he'd considered that name for New Horizons, but decided that the JFK reference might make Bush even more hostile to the probe than he then was -- only to have O'Keefe later give that name to the entire middle-price planetary-probe program.)

Anyway, the idea -- which in retrospect seems utterly cockamamie -- was to connect these three utterly different missions by using the same "core spacecraft" for each of them. Goldin then decided to make things even worse by overriding the recommendation of COMPLEX that the Pluto probe -- which, unlike the other two, actually required NO new technology -- fly first in 2003; he ordered instead that Europa Orbiter be flown before the Pluto mission. The result, naturally, was to delay the Pluto mission further and further as the impracticality of doing Europa Orbiter any time in the near future became obvious -- but I was told at the October 2000 meeting of the Solar System Exploration Subcommittee that Goldin told an aide that he had actually done this (along with insisting on totally impractical super-miniaturization of the Pluto probe) as a subterfuge for getting rid of the Pluto mission altogether, on the grounds that "Nobody gives a damn about Pluto."

This is where, to my lasting amazement, I enter the story. I did an August 2000 piece for "SpaceDaily" proposing that not only did the Pluto mission not require any new technologies at all (unlike the other parts of OP/SP), but that it could be flown much more cheaply by simply mildly modifying the design of either of the two existing Discovery comet probes, Stardust and CONTOUR. A month later, NASA surprised everyone by suddenly putting out an AO for ideas for a cheap Pluto probe design -- which they made very clear they were doing extremely grudgingly, and with no desire to really fly the thing.

When I got to the SSES meeting in October, there were stacks of my article on the information table; and on the first day two guys from Lockheed Martin got up and presented the company's proposal for modifying "Stardust" for the Pluto mission -- which reflected my own suggestions down to the very last goddamn detail, except that the launch would not be possible before December 2004 and so required a bigger booster than my suggested November 2003 launch. They told me later that Lockmart had come up with the idea completely independently, which I believe -- it had not exactly been a hard idea for me to come up with. But, to my stupefaction, although I had come to that meeting just as a reporter, I discovered that in the process of asking the assembled scientists for information on various subjects I was also GIVING them some information, and so Michael Drake ended up letting me take a bigger role in the debate over Pluto than he was legally supposed to do. While there was universal agreement that the argument for a near-future Pluto/Kuiper flyby was overwhelmingly strong, on the last day there was a debate over whether they might "anger NASA" by recommending it, and I ended up giving them a mini-Agincourt speech to the effect that their official job was simply to recommend the best scientific strategy for flying planetary missions, that the Pluto mission was clearly part of this, and that if NASA turned it down anyway for non-scientific reasons the agency had no reason to blame them for recommending it.

Whether this made a difference or not, they DID very strongly advocate the mission in their report, and the scientific pressure for it simply got stronger and stronger, until we finally had the spectacle -- almost unprecedented at the time -- of the GOP Congress telling not only NASA but the White House itself to go a kite, and ordering inclusion of money for the mission in the NASA budget. (The 2002 Decadal Survey report forcefully recommending it was probably the last impetus necessary for this.)

I'm still trying to determine just how important my role in all this actually was; but it seems certain that Simon Mansfield (the editor of "SpaceDaily) and I had SOME effect. I later learned that NASA was actually shutting up any engineer or scientist from publicly proposing an economically designed Pluto mission by threatening to cut off their grants, and so Simon and I ended up innocently belling the cat by publicly proposing the idea for the very first time and thus making it impossible for NASA to hush up the idea any longer. This may or may not have been what forced it to put out that reluctant AO for ideas on just this subject a month later; but judging from my treatment at that SSES meeting a month after that, my article played at least some contributing role in getting NASA's planned cancellation of any Pluto flyby mission reversed.

New Horizons, of course, IS based on CONTOUR -- although much more loosely than its competitor "POSSI" was based on Stardust -- but I can't believe that I inspired that idea; there were surely engineers already thinking about it. But -- because, by pure dumb chance, Simon and I happened to be in exactly the right place at the right time -- I did play a role in getting it flown. I take for granted that I will never get the chance to do anything remotely as important for the rest of my life. (Not that I've quite given up the hope that someday lightning might strike twice -- although my recent plan to push a penetrator as a small piggyback lander for Europa Orbiter turned out to have a subtle but very important flaw in it pointed out at the recent COMPLEX meeting. Oh, well. Back to the drawing board.)

Anyway, in retrospect it's perfectly obvious that Europa Orbiter was the most complex of the three OP/SP missions and should therefore have been flown last, with the Pluto flyby going first and Solar Probe second. Thanks entirely to Crazy Dan Goldin, this didn't happen -- or we could have seen the Pluto mission launched, with considerably lower cost and more science return, in November 2003 (which would even have allowed it to do a very close Io flyby en route!) And Solar Probe is STILL a very important mission -- in terms of practical human benefit, maybe the most important of the three -- and badly needs to be flown.
Bob Shaw
Bruce:

Careful there Ted, or Crazy Dan might try to pull strings to have you nominated as the command pilot of a (briefly) manned Solar mission!

Of course, he'd stand every chance of getting the second seat reservation for himself...

...I wonder who'd get the third slot?

Bob Shaw
Richard Trigaux
QUOTE (BruceMoomaw @ Dec 29 2005, 04:38 PM)
...I later learned that NASA was actually shutting up any engineer or scientist from publicly proposing an economically designed Pluto mission by threatening to cut off their grants... 


I hate this way to shut down any debate or new idea. There was another example about the technician who tried to warn about the hole into the shuttle heat shield... He was not heeded, with the result we know. Worse, in place of recognizing their mistake, the responsibles humiliated him in asking him to retract his view in public.

Ideas come at no cost, and they can make huge savings. So it is really a shame not to examine a given idea. And it is definitively not a shame if we are not the author of a good idea.
lyford
QUOTE (Bob Shaw @ Dec 29 2005, 08:45 AM)
Bruce:

Careful there Ted, or Crazy Dan might try to pull strings to have you nominated as the command pilot of a (briefly) manned Solar mission!

Of course, he'd stand every chance of getting the second seat reservation for himself...

...I wonder who'd get the third slot?

Bob Shaw
*

Perhaps Hotblack Desiato?
tty
QUOTE (kwan3217 @ Dec 29 2005, 07:05 AM)
1) Carry a large supply of carbon, and pump it out of the surface of your platform. The carbon vaporizes and carries off the heat. Use carbon since it has the highest known melting and vaporization temperature of any substance. It acts like an ablative heat shield, or as the story described it, the bottom layer of a water drop in a hot pan.
*



I wonder if the use of coal to absorb the heat has something to with an idea Freeman Dyson came up with when he was working on the Orion nuclear propulsion project. The problem was how to test the concept without breaking the test ban since the test needed to be done in vacuum.
Dyson’s idea was to do the test indoors in a very large vacuum chamber. This would be partly filled with hundreds of tons of charcoal blocks suspended on wires. The explosion would of course turn the charcoal into fine dust which would then absorb the energy from the explosion by being converted into gas. The pressure wouldn’t be excessive since most of the volume was originally vacuum and the energy would transfer relatively slowly to the chamber walls so they wouldn’t melt, at least not much. According to Dyson’s calculations the whole thing would only work for quite small nuclear explosions, up to a few tenths of a kiloton, but that was the range they were interested in for the Orion project anyway.

The idea apparently interested the AEC as well when they realized that if done in an underground cavity it would both prevent the escape of nuclear debris to the atmosphere and almost completely de-couple the explosion from the surrounding rock, thus making it possible to do undetectable nuclear tests. According to rumour it was actually tried in extreme secrecy in Nevada and worked more or less as intended. blink.gif

tty
punkboi
QUOTE (Richard Trigaux @ Dec 26 2005, 02:27 AM)
Not yet any Bush plan for Sun colonization?
*


Hahaha!! I'd say something...but I don't wanna turn this into a political topic.

EDIT: Okay, so I just browsed through the rest of this thread. I guess I didn't have to get political. tongue.gif
Bob Shaw
QUOTE (tty @ Dec 29 2005, 07:38 PM)
I wonder if the use of coal to absorb the heat has something to with an idea Freeman Dyson came up with when he was working on the Orion nuclear propulsion project. The problem was how to test the concept without breaking the test ban since the test needed to be done in vacuum.
Dyson’s idea was to do the test indoors in a very large vacuum chamber. This would be partly filled with hundreds of tons of charcoal blocks suspended on wires. The explosion would of course turn the charcoal into fine dust which would then absorb the energy from the explosion by being converted into gas.  The pressure wouldn’t be excessive since most of the volume was originally vacuum and the energy would transfer relatively slowly to the chamber walls so they wouldn’t melt, at least not much. According to Dyson’s calculations the whole thing would only work for quite small nuclear explosions, up to a few tenths of a kiloton, but that was the range they were interested in for the Orion project anyway.

The idea apparently interested the AEC as well when they realized that if done in an underground cavity it would both prevent the escape of nuclear debris to the atmosphere and almost completely de-couple the explosion from the surrounding rock, thus making it possible to do undetectable nuclear tests. According to rumour it was actually tried in extreme secrecy in Nevada and worked more or less as intended. blink.gif

tty
*



Freeman Dyson = Total JOY!

What a guy!

Bob Shaw
ljk4-1
QUOTE (Bob Shaw @ Jan 6 2006, 06:06 PM)
Freeman Dyson = Total JOY!

What a guy!

Bob Shaw
*


He is also pretty nifty at coming up with ways to utilize all of a star's energy:

http://www.orionsarm.com/civ/Dyson_Spheres.html
PhilHorzempa
The Solar Probe project is still alive. In a Report released on July 4, 2007,
regarding their actions on NASA's FY 2008 budget, the Senate
Appropriations Committee states the following - "The Committee
has included an additional $20,000,000 for the Living With A Star Program
for the Solar Probe mission."



Another Phil
Pando
http://solarprobe.gsfc.nasa.gov/
tedstryk
If it actually gets funded, it should also give us a nice Jupiter bonus. I am not sure about imaging (perhaps it will have a navigation camera or be able to catch Jupiter and its moons in one of its cameras intended for the sun like STEREO did), but I can't imagine them passing up the chance to at least have a Ulysses-style encounter, given the fact that this mission will certainly have its fair share of particle and fields instruments.
Y Bar Ranch
Hey, my first post here.

So my idea for a solar probe involves a super long tethered probe, spinning at a rate so as to have it's surface velocity with respect to the Sun be close to zero. The "mothership" would be far enough away to endure the environment. I know, extremely long tether...

Another thought I had would be a "floater", i.e., a probe with enough surface area that it took advantage of the flux of light and other stuff to suspend itself at a distance above the surface. It'd be a way of lowering the geosynchronous orbit altitude way down, or generally lowering the speed of the orbit. I didn't see any other concepts taking advantage of solar sails to assist in reaching the Sun.

Maybe the floater and the tether could be combined.
Geographer
What is the highest level of albedo that's been achieved with metals on Earth? If a shield had 100% reflectivity (impossible I know but theoretically), would that solve all heating problems, or does the albedo vary for different types of electromagnetic radiation?
JRehling
From one reference on the web, I'm seeing that aluminum has an albedo of 73%.

Suppose that tungsten had the same albedo. By my calculations, a surface of tungsten, then, would melt if held in steady state at about 0.17 AU.

However, there are a lot of other tricks that could be played to help out. A thin foil of tungsten would only take solar radiation on one side while radiating it on the other. Halving the thermal load should allow an approach sqrt(2) closer.

The sunscreen on SP is a long cone that would be pointed towards the Sun. That spreads out the radiation that a disk would absorb over a much greater area. I don't see any theoretical limit to this approach, although the point at the very tip might be a failure point. There would have to be SOME surface perpendicular to the Sun.

I guess if a maniacal plunge sunward were attempted with the goal of approaching as near as possible, one strategy would be to have a series of sunscreens, each of which had enough separation from the main craft so as not to radiate much heat inward, with each one shaded until the one in front of it melted through. If the final plunge were fast enough (if, say, a gravity assist of Jupiter really whipped the thing into the Sun, with all of the acceleration that would come with that last neck of the Sun's gravity well), it might make a lot of progress in those final hours during which the screens were melting one after another.

I wonder what the engineering limit would be. The corona? The point where gas actually contributed measurable friction? Since such a craft could easily be set up for a free return to Earth, could we run a solar sample return?!? I'm not sure if there's much point doing it from close-up versus collecting the solar wind farther out, but it's an exciting idea.
ngunn
Has anyone suggested using the phenomenon of total internal reflection in glass prisms? This is virtually 100 percent efficient.
ugordan
Wouldn't a big glass prism be massive?
ngunn
Lots of little ones forming a scaly skin? A cloud of detached beads in front of the spacecraft??

I dunno, just rambling. smile.gif
Juramike
Or how about ice crystals?

Could the probe squirt out a little water in front that would make a series of temporary shields of ice crystals? Could you design the atomizing device so that it would preferentially form ice crystals in the vacuum of space with maximum reflectivity? As it breaks down, would it also do decent job of absorbing heat?

(And water is relatively light to carry.)

So we'd be making an artificial comet!


(Really wildly speculating out there)
jamescanvin
I notice from reading this months BIS magazine (thanks for the free copy Phil wink.gif) that the Australians are now also proposing a solar probe like mission to get to within 3-4 solar radii. No clues as to how they intend to do it though.

ABC article
Juramike
QUOTE (jamescanvin @ Dec 11 2007, 09:23 AM) *
the Australians are now also proposing a solar probe like mission to get to within 3-4 solar radii. No clues as to how they intend to do it though.


Maybe they'll go at night? cool.gif
robspace54
I understand that Johns Hopkins University Applied Physics Lab (JHU/APL) has been studying the solar probe mission. The usual debates about mission capability, payload, and cost continue to swirl.

My source says that the various factions continue to not play nicely (scientists, NASA headquarters, Goddard, contractors) all of which wastes time, money and effort.

There was a Dilbert cartoon once (or perhaps a spoof) where the pointy-haired manager tells Dilbert that the spaceprobe weighs too much so he should delete the science instruments...

R.
djellison
Yeah - that was my series of (probably very illegal) 'spacebert' modifications to dilbert cartoons usually talking about Beagle 2 smile.gif
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